CN209868424U - Impact wrench - Google Patents

Abstract

The utility model relates to an electric tool technical field especially relates to an impact wrench, include: a drive motor; the driving shaft is connected with a motor shaft of the driving motor; the heavy hammer is axially and fixedly connected with the driving shaft, the heavy hammer is rotatably connected with the swinging block, the driving shaft is connected with the swinging block through the shifting mechanism, the heavy hammer and the driving shaft synchronously rotate under the non-impact condition, the driving shaft stops rotating under the impact condition, the heavy hammer rotates relative to the driving shaft by a preset angle under the inertia effect, and the swinging block rotates relative to the heavy hammer under the shifting of the driving shaft; and the output shaft is arranged in a central shaft hole of the heavy hammer in a penetrating mode, the outer side wall of the output shaft is provided with a protruding portion, and the swinging block rotates relative to the heavy hammer and is abutted against the protruding portion under the impact condition so as to transmit the rotation kinetic energy of the heavy hammer to the output shaft. The impact wrench can accelerate and decelerate through controlling the driving motor to output different output torques according to actual requirements, and the range of the output torque of the impact wrench is widened.

Description

Impact wrench

Technical Field

The utility model relates to an electric tool technical field especially relates to an impact wrench.

Background

The impact wrenches on the market are driven pneumatically or electrically, and the impact triggering method is triggered under a certain centrifugal force by using a mechanism with a spring, so that the torque output by the wrench is fixed, the same centrifugal force is always obtained near the same rotating speed, and the same torque is output.

SUMMERY OF THE UTILITY MODEL

In view of the above, it is necessary to provide an impact wrench aiming at the problem that the range of the output torque of the conventional impact wrench is small.

An impact wrench, comprising:

a drive motor for outputting a rotational drive force;

the driving shaft is connected with a motor shaft of the driving motor;

the heavy hammer is axially and fixedly connected with the driving shaft, the heavy hammer is rotatably connected with the swinging block, the driving shaft is connected with the swinging block through the shifting mechanism, the heavy hammer and the driving shaft synchronously rotate under the non-impact condition, the driving shaft stops rotating under the impact condition, the heavy hammer rotates relative to the driving shaft by a preset angle under the inertia effect, and the swinging block rotates relative to the heavy hammer under the shifting of the driving shaft; and

the output shaft is worn to establish in the center pin hole of weight, and the output shaft is located the partial lateral wall in the center pin hole of weight and is equipped with the bulge, and output shaft and weight rotate relatively under the non-impact condition, and the pendulum piece rotates for the weight and with the bulge butt under the impact condition to give the output shaft with the rotational kinetic energy transmission of weight.

In one embodiment, the driving shaft comprises a shaft sleeve, a connecting shaft is arranged in the center of the end face of the heavy hammer, the connecting shaft is inserted into the shaft sleeve, a sliding hole extending along the circumferential direction of the shaft sleeve is formed in the side wall of the shaft sleeve, a locking piece is arranged on the connecting shaft corresponding to the sliding hole and is arranged in the sliding hole in a sliding mode, and therefore the rotating angle range of the heavy hammer relative to the driving shaft is limited, and the axial fixing between the heavy hammer and the driving shaft.

In one embodiment, the impact wrench further comprises a return spring disposed between the weight and the drive shaft, the return spring for providing a return force to the weight when the weight is rotated relative to the drive shaft.

In one embodiment, the elastic return element comprises a torsion spring, the torsion spring is sleeved outside the connecting shaft, the heavy hammer is provided with a first clamping block used for being clamped between two torsion pins of the torsion spring, the driving shaft is provided with a second clamping block used for being clamped between the two torsion pins of the torsion spring, the driving shaft stops rotating under the impact condition, and the heavy hammer rotates relative to the driving shaft under the inertia effect by a preset angle to enable the two torsion pins of the torsion spring to be opened.

In one embodiment, the toggle mechanism comprises a toggle tooth part arranged on the driving shaft, and a half gear meshed with the toggle tooth part, wherein the half gear is connected to the end part of the rotating shaft of the swinging block.

In one embodiment, the side wall of the weight is provided with a containing groove communicated with the central shaft hole, and the swinging block is rotatably arranged in the containing groove.

In one embodiment, the cross section of the swinging block is arc-shaped, the inner arc of the swinging block is an arc concentric with the central shaft hole, the radius of the inner arc of the swinging block is larger than that of the central shaft hole under the non-impact condition, the swinging block rotates relative to the heavy hammer under the impact condition, and the vertical distance from one end point of the inner arc of the swinging block to the axis of the central shaft hole is smaller than the outer peripheral radius of the bulge.

In one embodiment, the impact wrench further comprises a coupling disposed between the motor shaft and the drive shaft, the drive shaft being coupled to the motor shaft via the coupling.

In one embodiment, the impact wrench further comprises a weight disposed on the weight, wherein the weight is used for balancing the weight.

In one embodiment, the drive motor is a brushless motor.

The beneficial effects of the utility model include:

the utility model discloses an impact wrench drives the weight through the drive shaft and begins with higher speed, when the driving motor rotational speed reaches the setting value, makes the driving motor brake, and drive shaft stall this moment, and the weight is because huge inertia can continue to rotate, consequently will produce relative rotation between drive shaft and the weight, and then the drive shaft passes through swing piece deflection on the drive weight of toggle mechanism. Meanwhile, the swinging block impacts the protruding part on the output shaft in the process that the heavy hammer continues to rotate, the heavy hammer stops instantly and transmits kinetic energy to the output shaft, and therefore the output shaft can output a large torque. The impact wrench has the advantage that the output torque of the output shaft is positively correlated with the rotating speed of the driving motor. When the set rotating speed of the driving motor is larger, the energy storage of the heavy hammer is more, the torque output by the output shaft is larger, and the output torque of the impact wrench is larger. Therefore, the utility model discloses an impact wrench accessible control driving motor's acceleration and deceleration comes to realize impacting the different output torque of spanner output according to actual need, widens the scope of the output torque who strikes the spanner.

Drawings

Fig. 1 is an exploded view of an impact wrench according to an embodiment of the present invention;

fig. 2 is a schematic view illustrating the structural assembly of an impact wrench according to an embodiment of the present invention;

FIG. 3 is a schematic top view of the structure of FIG. 2;

FIG. 4 is a schematic view of the cut-away A-A of the structure of FIG. 3 in a non-impact condition;

FIG. 5 is a schematic view of the structure of FIG. 3 taken at section A-A during an impact event;

fig. 6 is a flowchart illustrating a control method for an impact wrench according to an embodiment of the present invention;

fig. 7 is a flowchart of a control method for an impact wrench according to another embodiment of the present invention;

fig. 8 is a graph of the rotation speed of the driving motor and the output torque of the impact wrench according to an embodiment of the present invention.

Description of reference numerals:

10-impact wrench;

100-a drive motor; 110-a motor shaft;

200-a drive shaft;

210-a shaft sleeve; 211-a slide hole;

220-a second fixture block;

300-weight dropper;

310-a wobble block; 320-a connecting shaft; 321-a locking member;

330-a first fixture block; 340-accommodating grooves;

400-a toggle mechanism;

410-a poke tooth part; 420-half gear;

500-an output shaft;

510-a projection;

600-torsion spring;

700-a coupler;

800-a balancing weight;

900-Heat dissipation Fan.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the impact wrench of the present invention will be further described in detail by embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the invention.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only.

Referring to fig. 1, an impact wrench 10 according to an embodiment of the present invention includes a driving motor 100, a driving shaft 200, a weight 300, and an output shaft 500. The drive motor 100 is used to output a rotational drive force. The driving shaft 200 is connected to the motor shaft 110 of the driving motor 100. The weight 300 is axially fixedly connected with the driving shaft 200, the weight 300 is rotatably connected with the swinging block 310, the driving shaft 200 is connected with the swinging block 310 through the toggle mechanism 400, the weight 300 and the driving shaft 200 rotate synchronously under the non-impact condition, the driving shaft 200 stops rotating under the impact condition, the weight 300 rotates relative to the driving shaft 200 by a preset angle under the inertia effect, and the swinging block 310 rotates relative to the weight 300 under the toggle action of the driving shaft 200. The output shaft 500 is inserted into the central axial hole of the weight 300, and the outer sidewall of the portion of the output shaft 500 located in the central axial hole of the weight 300 is provided with a protrusion 510, so that the output shaft 500 and the weight 300 rotate relative to each other in the non-impact condition, and the swing block 310 rotates relative to the weight 300 and abuts against the protrusion 510 in the impact condition, so as to transmit the rotational kinetic energy of the weight 300 to the output shaft 500.

The specific implementation mode is as follows: the driving motor 100 drives the driving shaft 200 to rotate and further drives the weight 300 to start accelerating, when the rotation speed of the driving motor 100 reaches a set value, the driving shaft 100 is braked, at this time, the driving shaft 200 stops rotating, and the weight 300 continues to rotate due to huge inertia, so that relative rotation is generated between the driving shaft 200 and the weight 300, and further the driving shaft 200 drives the swing block 310 on the weight 300 to deflect through the toggle mechanism 400. While the weight 300 continues to rotate, the swing block 310 hits the protrusion 510 of the output shaft 500, the weight 300 stops momentarily and transmits kinetic energy to the output shaft 500, and the output shaft 500 can output a large torque. It will be appreciated that the magnitude of the torque output by the impact wrench 10 is positively correlated to the rotational speed of the drive motor 100. When the set rotation speed of the driving motor 100 is larger, the more energy is stored in the weight 300, the larger the torque output by the output shaft 500, i.e., the larger the output torque of the impact wrench 10. Therefore, the utility model discloses the acceleration and the speed reduction of impact wrench 10 accessible control driving motor 100, come according to actual need to realize impacting the different output torque of wrench 10 output, widen the scope of the output torque of impact wrench 10.

The impact wrench 10 of the embodiment of the present invention drives the driving motor 100 to rotate the weight 300 in an accelerated mannerWhen the machine 100 reaches a certain rotation speed, the energy of the rotation of the weight 300 is:where J is the moment of inertia of the weight and ω is the angular velocity. At this time, if the swing block 310 of the trigger weight 300 rotates so that the weight 300 collides with the protrusion 510 of the output shaft 500 through the swing block 310, the weight 300 can transmit energy to the output shaft 500. Usually, the weight 300 accelerates for a period of time in the order of seconds, and the impact process time is very short, so the weight 300 can instantly release the stored energy in several seconds to the output shaft 500, so that the output shaft 500 obtains a large torque for tightening or loosening the large bolt.

Among them, the driving motor 100 may be a brushless motor. The brushless motor is more flexible to drive than the conventional motor, and the acceleration and deceleration processes of the brushless motor are easily controlled by a software program, so that the impact wrench 10 can output different output torques according to actual requirements.

Referring to fig. 1, as an implementation manner, the driving shaft 200 includes a shaft sleeve 210, and a connecting shaft 320 is disposed at the center of an end surface of the weight 300, and the connecting shaft 320 is inserted into the shaft sleeve 210. The side wall of the sleeve 210 is provided with a sliding hole 211 extending along the circumferential direction of the sleeve 210, and the connecting shaft 320 is provided with a locking member 321 corresponding to the sliding hole 211. The locking member 321 is slidably disposed in the slide hole 211, thereby defining an angular range of rotation of the weight 300 relative to the driving shaft 200 and achieving axial fixation between the weight 300 and the driving shaft 200. The locking member 321 may be a screw threadedly coupled to the coupling shaft 320. Or the locking member 321 may be a latch inserted on the connecting shaft 320. Specifically, when assembling the driving shaft 200 and the weight 300, the connecting shaft 320 may be inserted into the sleeve 210, and the locking member 321 may be inserted through the sliding hole 211 and fixed to the connecting shaft 320. Through the shaft sleeve 210, the connecting shaft 320, the sliding hole 211 and the locking piece 321, the axial fixation and the relative rotation between the driving shaft 200 and the weight 300 are easy to realize, the structure is simple, and the assembly and the disassembly are easy.

Referring to fig. 1, in one embodiment, the impact wrench 10 further includes a return spring disposed between the weight 300 and the driving shaft 200 for providing a return force to the weight 300 when the weight 300 rotates relative to the driving shaft 200. The elastic restoring element can be a spring, an elastic rope, a torsion spring and the like. Through the elastic component that resets, can guarantee under the non-impact condition that weight 300 and drive shaft 200's position relatively fixed to realize that driving motor 100 drives drive shaft 200 and weight 300 synchronous revolution.

Further, the elastic return element includes a torsion spring 600, and the torsion spring 600 is sleeved outside the connecting shaft 320. The weight 300 is provided with a first latch 330 for being caught between the two torsion legs of the torsion spring 600, and the driving shaft 200 is provided with a second latch 220 for being caught between the two torsion legs of the torsion spring 600. When the driving shaft 200 stops rotating under the impact condition, the weight 300 rotates by a predetermined angle relative to the driving shaft 200 under the inertia effect, and at this time, the first latch 330 on the weight 300 and the second latch 220 on the driving shaft 200 are misaligned with each other, so that the two torsion legs of the torsion spring 600 are opened, and the torsion spring 600 accumulates the restoring force. When the swing block 310 hits the output shaft 500 to stop the weight 300 instantly, the first latch 330 of the weight 300 can return to the position opposite to the second latch 220 of the driving shaft 200 under the returning force provided by the torsion spring 600, and the weight 300 is returned.

The swing block 310 may be rotatably disposed on the weight 300. Referring to fig. 1 and 2, as an implementation manner, the side wall of the weight 300 is formed with a receiving groove 340 communicating with the central shaft hole, and the swing block 310 is rotatably mounted in the receiving groove 340. Specifically, the swing block 310 is fixed to the rotation shaft, and shaft holes are formed at opposite sidewalls of the receiving groove 340 of the weight 300. The swinging block 310 is rotatably mounted in the receiving groove 340 by the cooperation of the rotating shaft and the shaft hole. Referring to fig. 3 to 5, further, the cross section of the swing block 310 has an arc shape, and the inner arc of the swing block 310 is an arc concentric with the central shaft hole. As shown in FIG. 4, the radius of the inner arc of the swing block 310 is greater than the radius of the central shaft bore in the non-impact condition. When the driving motor 100 is started, the driving shaft 200 and the weight 300 are driven to rotate synchronously, and the output shaft 500 does not rotate along with the weight 300. As shown in FIG. 5, in the event of an impact, the swing block 310 rotates relative to the weight 300, and the perpendicular distance from one of the end points of the inner arc of the swing block 310 to the axis of the central shaft hole is smaller than the outer peripheral radius of the protrusion 510. Therefore, during the process of continuing the rotation of the weight 300, the swing block 310 will hit the protrusion 510 on the output shaft 500, the weight 300 will stop instantly and transmit the kinetic energy to the output shaft 500, so that the output shaft 500 can output a large torque.

The position of the swing block 310 in fig. 5 is obtained by rotating the swing block 310 of fig. 4 clockwise by a certain angle. It can be understood that the swing block 310 has a symmetrical structure, and when the swing block 310 rotates counterclockwise, the upper end of the swing block 310 will hit the protrusion 510 while the weight 300 continues to rotate. Therefore, the driving motor 100 can rotate in both forward and reverse directions to impact the weight 300 on the output shaft 500, thereby performing the impact function of the impact wrench 100.

The toggle mechanism 400 may be configured in a variety of ways. Referring to fig. 1 and 2, in one embodiment, the toggle mechanism 400 includes a toggle tooth portion 410 disposed on the drive shaft 200, and a half gear 420 engaged with the toggle tooth portion 410, the half gear 420 being connected to an end of the rotation shaft of the swing block 310. In case of impact, the driving shaft 200 stops rotating, and when the weight 300 rotates by a preset angle relative to the driving shaft 200 under the inertia effect, the tooth poking part 410 pokes the swing block 310 through the half gear 420 to rotate the swing block 310, so that the swing block 310 can abut against the protrusion 510 to impact the output shaft 500. In other embodiments, the toggle mechanism 400 may further include a rack gear disposed on the driving shaft 200 and a gear engaged with the rack gear, the gear being coupled to the end of the rotation shaft of the swing block 310.

Referring to fig. 1, as one practical way, the impact wrench 10 further includes a coupling 700 disposed between the motor shaft 110 and the driving shaft 200, and the driving shaft 200 is connected to the motor shaft 110 through the coupling 700. Through the coupling 700, not only the connection and power transmission between the motor shaft 110 and the driving shaft 200 are realized, but also the high alignment of the motor shaft 110 and the driving shaft 200 can be ensured to transmit a large torque.

Referring to fig. 1, as an implementation manner, the impact wrench 10 further includes a weight 800 disposed on the weight 300, and the weight 800 is used for balancing the weight 300. Through the counterweight 800, the weight 300 can be balanced, so that the gravity center of the weight 300 can be located on the rotation axis of the weight 300, and the stability of the rotation of the weight 300 can be ensured.

In one embodiment, the impact wrench 10 may also include some conventional structure such as a housing, a heat sink fan 900, and the like. The driving motor 100, the driving shaft 200, the weight 300 and the output shaft 500 are all disposed in the housing, and the output shaft 500 protrudes out of the housing. The heat dissipation fan 900 is disposed in the housing. Fig. 1 is an exploded view of an impact wrench 10 according to an embodiment of the present invention, and fig. 1 shows a heat dissipation fan 900 (the heat dissipation fan 900 is omitted from the assembly view of fig. 2). As shown in fig. 1, a heat sink fan 900 may be attached to the motor shaft 110, the heat sink fan 900 being used to dissipate heat from within the housing when the impact wrench 10 is in operation. It is understood that the housing may be provided with heat dissipation windows accordingly.

Referring to fig. 6 and 7, an embodiment of the present invention further provides a control method of the impact wrench, for controlling the impact wrench 100. The control method comprises the following steps: the driving shaft 200 and the weight 300 are driven by the driving motor 100 to synchronously rotate, and when the rotating speed of the driving motor 100 reaches a preset value, the driving motor 100 is controlled to stop outputting the torque. At this time, the driving shaft 200 stops rotating, and the weight 300 rotates by a preset angle relative to the driving shaft 200 by inertia, so that the weight 300 strikes the output shaft 500 through the swinging block 310, and the output shaft 500 outputs torque. It can be understood that when the rotation speed of the driving motor 100 is higher, the more energy is stored in the weight 300, the higher the torque output by the output shaft 500, i.e. the higher the output torque of the impact wrench 10 is. Therefore, the utility model discloses a control method accessible control driving motor 100 accelerates and decelerates, comes to realize according to actual need that impact wrench 10 exports different output torque, widens the scope of the output torque of impact wrench 10.

And there are various ways in which the rotation speed of the driving motor 100 can reach the preset value. Referring to fig. 6, as an implementable manner, the control method of the impact wrench further includes the steps of: the output torque is preset by the first adjusting device. A signal corresponding to the torque value is read by the control device. The control device calculates the rotation speed required to be output by the driving motor 100 according to the torque signal, and controls the driving motor 100 to operate to the required rotation speed. In this embodiment, the output torque of the impact wrench is preset, and then the rotation speed that the driving motor 100 needs to output is calculated, and the driving motor 100 is controlled to operate to the required rotation speed, that is, the rotation speed of the driving motor 100 reaches the preset value, at this time, the driving motor 100 is controlled to stop, so that the impact wrench 10 can output the torque of the set magnitude.

In one embodiment, the first adjustment device includes a knob potentiometer having a plurality of different torque steps. The user accessible rotates the knob potentiometre and sets up the moment of torsion gear, and the knob potentiometre can produce corresponding torque signal and transmit for controlling means, and then controlling means can this torque signal calculate the rotational speed that driving motor 100 needs to be exported to control driving motor 100 and move to required rotational speed. In other embodiments, the first adjustment device may also be set digitally, with a specific torque being set by a button to generate a corresponding torque signal.

Referring to fig. 7, as another practicable manner, the control method of the impact wrench further includes the steps of: the output rotational speed is preset by the second regulating device. The signal corresponding to the rotational speed value is read by the control device. The driving motor 100 is controlled by the control device to operate to the required rotation speed according to the rotation speed signal. In this embodiment, the output rotation speed of the driving motor 100 is preset, and the control device controls the driving motor 100 to operate to the required rotation speed, that is, the rotation speed of the driving motor 100 reaches the preset value, and at this time, the driving motor 100 is controlled to stop, so that the impact wrench 10 can output the torque with the required magnitude.

In one embodiment, the second adjustment device comprises a knob potentiometer having a plurality of different rotational speed steps. The user can set up the rotational speed gear through rotatory knob potentiometre, and the knob potentiometre can produce corresponding rotational speed signal and transmit for controlling means, and then controlling means can this rotational speed signal control driving motor 100 move to required rotational speed. In other embodiments, the second adjustment device may also be set digitally, with a specific speed being set by a button to generate a corresponding speed signal.

The utility model discloses impact wrench's control method can set for different gears (rotational speed gear or moment of torsion gear) through the knob potentiometre, and then obtains different output torque value. A typical speed versus output torque value table is as follows:

referring also to fig. 8, fig. 8 shows a graph of rotational speed of the drive motor of the impact wrench versus output torque value. It can be seen that the torque output from the output shaft 500, i.e., the output torque of the impact wrench 10, increases as the rotation speed of the driving motor 100 increases. Therefore, the utility model discloses a control method accessible control driving motor 100 accelerates and decelerates, comes to realize according to actual need that impact wrench 10 exports different output torque, widens the scope of the output torque of impact wrench 10.

Referring to fig. 6 and 7, as an implementable manner, the control method of the impact wrench further includes the steps of: the actual rotational speed of the drive motor 100 is detected by the detection device and a corresponding rotational speed signal is sent to the control device. The actual rotational speed is compared with the desired rotational speed by the control device to generate a control signal that causes the rotational speed of the drive motor 100 to approach the desired rotational speed. In this embodiment, the rotating speed of the driving motor 100 is detected in real time by the detecting device, and the corresponding rotating speed signal is transmitted to the control device, and the control device can adjust in time after comparison so that the actual rotating speed of the driving motor 100 is consistent with the required rotating speed. In one embodiment, the detection means comprises a speed sensor, which is connected to the control means. The speed sensor is used to sense the rotational speed of the motor shaft 110 of the driving motor 100 and transmit a corresponding signal to the control device. The speed sensor may be one of an inductive sensor, a hall sensor, and a photo sensor.

Further, the control means includes an electric control switch for starting or stopping the driving motor 100 according to a user operation. The electric control switch may be a forward/reverse switch, and the forward/reverse switch may control the driving motor 100 to rotate forward or reverse.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only represent some embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims (10)

1. An impact wrench, comprising:

a drive motor for outputting a rotational drive force;

a driving shaft connected with a motor shaft of the driving motor;

the weight is axially fixedly connected with the driving shaft, the weight is rotatably connected with a swinging block, the driving shaft is connected with the swinging block through a toggle mechanism, the weight and the driving shaft rotate synchronously in a non-impact condition, the driving shaft stops rotating in an impact condition, the weight rotates relative to the driving shaft by a preset angle under the action of inertia, and the swinging block rotates relative to the weight under the toggle action of the driving shaft; and

the output shaft is arranged in a central shaft hole of the heavy hammer in a penetrating mode, a protruding portion is arranged on the outer side wall of the portion, located in the central shaft hole of the heavy hammer, of the output shaft, the output shaft and the heavy hammer rotate relatively under the non-impact condition, and the swinging block rotates relative to the heavy hammer and can abut against the protruding portion under the impact condition, so that the rotating kinetic energy of the heavy hammer is transmitted to the output shaft.

2. The impact wrench as claimed in claim 1, wherein said driving shaft includes a sleeve, said weight has a connecting shaft at the center of its end surface, said connecting shaft is inserted into said sleeve, said sleeve has a side wall with a sliding hole extending along the circumference of said sleeve, said connecting shaft has a locking member corresponding to said sliding hole, said locking member is slidably disposed in said sliding hole, thereby limiting the angular range of rotation of said weight relative to said driving shaft and achieving axial fixation between said weight and said driving shaft.

3. The impact wrench of claim 2, further comprising a return spring disposed between the weight and the drive shaft, the return spring configured to provide a return force to the weight when the weight is rotated relative to the drive shaft.

4. The impact wrench as claimed in claim 3, wherein said resilient return member comprises a torsion spring, said torsion spring is disposed around said connecting shaft, said weight is provided with a first engaging portion for engaging between two legs of said torsion spring, said driving shaft is provided with a second engaging portion for engaging between two legs of said torsion spring, said driving shaft stops rotating in case of impact, and said weight is rotated by a predetermined angle relative to said driving shaft under inertia to open the two legs of said torsion spring.

5. The impact wrench of claim 1, wherein the toggle mechanism includes a toggle portion disposed on the drive shaft, and a half-gear engaged with the toggle portion, the half-gear being connected to a rotating shaft end of the swing block.

6. The impact wrench as claimed in claim 1, wherein said weight has a side wall defining a receiving groove communicating with said central axis hole, said oscillating block being rotatably mounted in said receiving groove.

7. The impact wrench as claimed in claim 6, wherein said swinging block has an arc-shaped cross section, an inner arc of said swinging block is an arc concentric with said central shaft hole, a radius of said inner arc of said swinging block is larger than a radius of said central shaft hole in a non-impact condition, said swinging block rotates relative to said weight in an impact condition, and a perpendicular distance from one end point of said inner arc of said swinging block to an axis of said central shaft hole is smaller than a radius of an outer periphery of said protrusion.

8. The impact wrench of claim 1, further comprising a coupling disposed between the motor shaft and the drive shaft, the drive shaft being connected to the motor shaft by the coupling.

9. The impact wrench of claim 1, further comprising a weight disposed on the weight, the weight being configured to balance the weight.

10. The impact wrench of claim 1, wherein the drive motor is a brushless motor.